In recent years, the areas of the electrode terminals of a semiconductor chip and a center distance between adjacent electrode terminals in a semiconductor chip have been reduced (smaller pitches of the electrode terminals) so as to increase the density of semiconductor chips and the number of pins on the electrode terminals of the semiconductor chips.
Typically, in flip-chip packaging, semiconductor chips such as an LSI are mounted face down on a mounting substrate. Specifically, protruding electrodes such as solder bumps are formed on the electrode terminals of a semiconductor chip, and then the protruding electrodes' are heated and pressed to the electrode terminals of the mounting substrate. This forms bump connections.
Generally, electrode terminals are disposed on the outer periphery of a semiconductor chip. However, a center distance between adjacent electrode terminals has been considerably reduced and thus if electrode terminals are only disposed on the outer periphery of a semiconductor chip, a short circuit may occur between the electrode terminals or a faulty connection may be caused by a difference in thermal expansion coefficient between the semiconductor chip and a mounting substrate.
To address this problem, electrode terminals have been disposed over the electrode surfaces of semiconductor chips (area layout). The layout of the electrode terminals can increase a center distance (the pitch of the electrode terminals) between the adjacent electrode terminals. In recent years, however, a center distance between adjacent electrode terminals has been considerably reduced also in the layout of electrode terminals disposed over the electrode surface of a semiconductor chip.
Solder bumps are generally formed by the following method: first, solder is supplied onto electrode terminals by screen printing, a dispenser, or electrolytic plating, and then the supplied solder is heated at least to the melting point of solder in a reflow furnace. This forms protruding solder bumps on the electrode terminals.
In recent years, however, a center distance between adjacent solder bonding sections (the pitches of solder bonding sections) has been further reduced. Additionally, a clearance between a semiconductor chip and a mounting substrate has been also reduced. This may cause problems such as a “faulty solder bridge”. Such a “faulty solder bridge” is caused by molten solder deformed so as to join solder bumps with a solder surface tension in the heating step of flip-chip packaging. In order to solve such a “faulty solder bridge”, a bump having a two-layer structure has been proposed so as to reduce the amount of solder. For example, in Patent Literature 1, proposed bumps each have a two-layer structure composed of an insulating coating containing metallic particles over the surface of a protruding electrode made of gold or copper. The proposed bumps prevent the insulating coating and the protruding electrode from melting during flip-chip packaging, thereby avoiding the occurrence of “faulty solder bridges”. This allows a smaller center distance between adjacent electrode terminals. The bumps disclosed in Patent Literature 1 are electrically connected to the electrode terminals of a mounting substrate by a force generated in the compressing direction of molding resin when the molding resin injected between a semiconductor chip and the mounting substrate hardens and shrinks.
In recent years, however, a smaller center distance between adjacent electrode terminals has been required. Thus, the areas of the electrode terminals have been reduced. If the bumps disclosed in Patent Literature 1 are used in a semiconductor chip, metallic particles in the insulating coating are not diffusion bonded to the protruding electrodes (metal electrodes) of the semiconductor chip or the electrode terminals (metal electrodes) of a mounting substrate. The protruding electrodes of the semiconductor chip and the electrode terminals of the mounting substrate are electrically connected to each other only by bringing metallic particles in the insulating coating into contact with the protruding electrodes (metal electrodes) of the semiconductor chip and the electrode terminals (metal electrodes) of the mounting substrate. Thus, if the areas of the electrodes are reduced, the number of conductive particles decreases between the protruding electrodes of the semiconductor chip and the electrode terminals of the mounting substrate, disadvantageously increasing a connection resistance and a signal transmission loss.
To address this problem, recent bumps each have a two-layer structure including a solder upper metal on a lower metal composed of a refractory metal (For example, see Patent Literature 2). The bump having the two-layer structure can reduce the amount of solder as compared to a single-layer bump only made of solder. This reduces the amount of solder protruding in a plane direction during flip-chip packaging, thereby preventing the occurrence of solder bridges. Furthermore, the solder of the upper metal is diffusion bonded to the lower metal (protruding electrodes) provided on a semiconductor chip and the electrode terminals of a mounting substrate. This reduces a connection resistance and does not increase a signal transmission loss.